‘Sacrificial’ supramolecular assembly and pressure-induced polymerization: toward sequence-defined functionalized nanothreads

“…Nanothreads were first synthesized from benzene under pressure in diamond anvil cells or Paris-Edinburgh cells, 3,4 but the high-pressure solid-state synthesis technique appears to be quite general for unsaturated hydrocarbons. To date, nanothreads have been synthesized from benzene, 3,4 pyridine, 5 aniline, 6 a naphthalene/octafluoronaphthalene cocrystal, 7 thiophene, 8 cubane, 9 and very recently a phenol/pentafluorophenol cocrystal, 10 and furan. 11 It is expected that more polymers of this kind are coming, and that sample sizes of certain threads will rapidly expand as synthesis pressures continue to fall.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Studies of Furan and Thiophene Nanothreads: Structures, Cycloaddition Barriers and Activation Volumes

Chen

Crespí²,

Hoffmann³

2021

Preprint

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In this theoretical study we examine several aspects of the formation, structure, and stability of the most ordered nanothreads yet made, those derived from furan and thiophene. First, we look at the enthalpic consequences and activation barriers of the first two steps of oligomerization by a Diels-Alder mechanism. The ca. 20 GPa difference in the synthetic pressures (furan lower) is explainable in terms of greater loss of aromaticity by the thiophene. Subsequent steps have understandably lower barriers. We show explicitly how pressure affects the reaction profiles, operating through the volume decrease in the transition state and onward to the product molecule. The interesting option of polymerization proceeding in one or two directions opens up the possibility of polymers with two opposing and cumulative dipole moments. The computed activation volumes are consistently more negative for likely initial furan (compared with thiophene) polymerization steps, in accord with the lower onset pressure of furan polymerization. In the second part of our study we examine the energetics of the likely polymers. Three ordered polymer structures compete in enthalpy -- a syn one, with all O/S on the same side, an anti one, S/O alternating, and a syn-anti isomer, with segments of four monomers repeating. The syn polymer, if not allowed to distort, is at high enthalpy relative to the other two. The origin of the destabilization is apparent, being S/O lone-pair repulsion, understandably greater for S than O at the 2.8/2.6Å separation. Set free, the syn isomers curve or arc, in two- or three-dimensional (helical) ways, whose energetics are traced in detail. The syn polymer can also stabilize itself by the thread twisting into zig-zag or helical enthalpic minima. Release of strain in a linear thread as the pressure is relaxed to 1 atm, with consequent thread curving, is a likely mechanism for the observed loss of crystalline order in the polymer as it is returned to ambient pressure.

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“…This reduced amount of conformational freedom can help enhance the folding of aromatic polymers, to advance a variety of useful properties such as selective supramolecular recognition (Goodman et al, 2007;Liu et al, 2015;Otte, 2016;Schneebeli et al, 2016;Adhikari et al, 2017;Xie et al, 2020), selective catalysis (Rajappan et al, 2020;Sharafi et al, 2020), and self-assembly (Cole et al, 2017;Greene et al, 2017;Bonduelle, 2018;Ong and Swager, 2018;Delawder et al, 2019;Zhao et al, 2019). However, while the precise chemical structures, lengths, and sequences of such macromolecules (Dobscha et al, 2019;Gerthoffer et al, 2020;Zhao et al, 2020) dictate their folding, and with it their functionalities and physical properties (Chen et al, 2015;Hanlon et al, 2017), it remains challenging to synthesize polyaromatic structures with precise lengths and/or sequences as unimolecular entities. One of the most efficient ways to precisely control the length and sequence of synthetic polymers is by iteratively coupling (Jones et al, 1997) polymer strands together in a convergent/divergent fashion (Hawker et al, 1997;Read et al, 2000;Grayson and Frechet, 2001;Li et al, 2005;Liess et al, 2006;Binauld et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Iterative Exponential Growth of Oxygen-Linked Aromatic Polymers Driven by Nucleophilic Aromatic Substitution Reactions

et al. 2021

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This work presents the first transition metal-free synthesis of oxygen-linked aromatic polymers by integrating iterative exponential polymer growth (IEG) with nucleophilic aromatic substitution (SNAr) reactions. Our approach applies methyl sulfones as the leaving groups, which eliminate the need for a transition metal catalyst, while also providing flexibility in functionality and configuration of the building blocks used. As indicated by 1) 1H-1H NOESY NMR spectroscopy, 2) single-crystal X-ray crystallography, and 3) density functional theory (DFT) calculations, the unimolecular polymers obtained are folded by nonclassical hydrogen bonds formed between the oxygens of the electron-rich aromatic rings and the positively polarized C–H bonds of the electron-poor pyrimidine functions. Our results not only introduce a transition metal-free synthetic methodology to access precision polymers but also demonstrate how interactions between relatively small, neutral aromatic units in the polymers can be utilized as new supramolecular interaction pairs to control the folding of precision macromolecules.

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‘Sacrificial’ supramolecular assembly and pressure-induced polymerization: toward sequence-defined functionalized nanothreads

Abstract: Limited supramolecular strategies have been utilized to synthesize sequence-defined polymers, despite the prominence of noncovalent interactions in materials design. Herein, we illustrate the utility of ‘sacrificial’ aryl-perfluoroaryl supramolecular synthons to...

Cited by 27 publications

References 26 publications

Mechanistic insights into the pressure-induced polymerization of aryl/perfluoroaryl co-crystals

Mechanistic insights into the pressure-induced polymerization of aryl/perfluoroaryl co-crystals

Theoretical Studies of Furan and Thiophene Nanothreads: Structures, Cycloaddition Barriers and Activation Volumes

Iterative Exponential Growth of Oxygen-Linked Aromatic Polymers Driven by Nucleophilic Aromatic Substitution Reactions

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